Method for controlling a steer-by-wire steering system and steer-by-wire steering system for a motor vehicle

Abstract

A method for controlling a steer-by-wire steering system involves determining a torque request signal with a position controller based on desired and actual steering angles, checking with a checking device for an error state of the position controller, selecting the torque request signal as a checked torque request signal if the error state has not been determined, selecting a reference torque signal as the checked torque request signal if the error state has been determined, and transmitting the checked torque request signal to the steering actuator. By evaluating a cumulative deviation variable, which is calculated by a calculation unit of the checking device as a time integral over a control deviation between the desired and actual steering angles, the checking device determines whether the error state is present and determines the reference torque signal with a reference controller based on the control deviation.

1 .- 10 . (canceled). 
     
     
         11 . A method for controlling a steer-by-wire steering system for a motor vehicle comprising an electronically controllable steering actuator that acts on steered wheels and that detects an actual steering angle of the steered wheels, a feedback actuator that detects a desired steering angle set via a steering wheel, and an activation unit that activates the electronically controllable steering actuator in accordance with the desired steering angle and the actual steering angle with a checked torque request signal, wherein the method comprises:
 determining a torque request signal by a position controller of the activation unit based at least on the desired steering angle and the actual steering angle;   checking with a checking device of the activation unit whether there is an error state of the position controller;   selecting the torque request signal as the checked torque request signal with a selection device of the checking device if the error state has not been determined;   selecting a reference torque signal as the checked torque request signal with the selection device of the checking device if the error state has been determined; and   transmitting the checked torque request signal to the steering actuator; and   evaluating a cumulative deviation variable, which is calculated by a calculation unit of the checking device as a time integral over a control deviation between the desired steering angle and the actual steering angle, to enable the checking device to determine whether the error state is present and determine the reference torque signal by way of a reference controller based at least on the control deviation.   
     
     
         12 . The method of  claim 13  wherein the cumulative deviation variable is calculated by weighting the control deviation with a driving speed of the motor vehicle. 
     
     
         13 . The method of  claim 13  comprising determining the error state of the position controller when the cumulative deviation variable exceeds a selectable threshold value. 
     
     
         14 . The method of  claim 13  comprising selecting the selectable threshold value based on a driving speed of the motor vehicle. 
     
     
         15 . The method of  claim 13  comprising taking into account a momentary angular velocity of the steering actuator when determining the reference torque signal by the reference controller. 
     
     
         16 . The method of  claim 15  wherein the reference torque signal contains a component proportional to the control deviation and a component dependent on the momentary angular velocity of the steering actuator. 
     
     
         17 . The method of  claim 13  wherein the selection device switches back from the reference torque signal to the torque request signal as the checked torque request signal after a predetermined period of time has elapsed after the error state has been determined. 
     
     
         18 . The method of  claim 17  wherein while the selection device is switching, the selection device interpolates the checked torque request signal between the reference torque signal and the torque request signal. 
     
     
         19 . The method of  claim 13  wherein the selection device switches back from the reference torque signal to the torque request signal as the checked torque request signal after at least one of the reference torque signal or the torque request signal falls below a specifiable threshold value. 
     
     
         20 . The method of  claim 19  wherein while the selection device is switching, the selection device interpolates the checked torque request signal between the reference torque signal and the torque request signal. 
     
     
         21 . A steer-by-wire steering system comprising:
 an electronically controllable steering actuator that acts on steered wheels and via which an actual steering angle of the steered wheels is detectable;   a feedback actuator with which a desired steering angle set via a steering wheel is detectable; and   an activation unit for activating the electronically controllable steering actuator according to the desired steering angle and the actual steering angle by way of a checked torque request signal,   wherein the activation unit contains a position controller and a checking device with a selection device, wherein the checking device contains a reference controller and a calculation unit and is configured to perform the method of  claim 13 .